1. Field of the invention
The present invention relates to a flat-plate multiplex antenna which operates at least two frequency bands, and a portable terminal such as a portable telephone (includes PHS), a mobile wireless device, a note type personal computer and so on, and more specifically, to a flat-plate multiplex antenna that is small in size, wide in band and possible to operate at least two frequency band and a portable terminal using it.
2. Prior Art
Recently, accompanied with high performance of communication, a portable terminal which is possible to operate at two frequency bands is used practically.
A conventional antenna for use in a portable terminal is shown in FIG. 1. This antenna 50 comprising a radiating conductor 52 provided with a slit 51 having a J shaped slit portion 51a and an open slit portion 51b of which one end is opened, and being uniform slit width, a dielectric 53 provided to whole reverse side of the radiating conductor 53, and a feeder line 54a, 54b which supplies power to the radiating conductor 52.
According to the conventional antenna, adjustment of band by widening a slit width is almost impossible, because when a slit width is widened, band extends but resonant point moves to high frequency, and resonant point is moved to low frequency by widening position. Accordingly, antenna characteristic was adjusted by varying slit length with slit width is constant. Therefore, extending of band was limited. On the other hand, it is possible to extend band by enlarging antenna size (volume), but it becomes difficult to comply with demand to compactness.